John McDonnell is just late enough for this evening's political gathering in Hackney to spark a few nervous cellphone calls from a few nervous organisers. 'He's on his way,' they report to the crowd after the first call. 'He's probably underground,' they say after several attempts at a second. 'He's at Bethnal Green tube station waiting for a taxi,' they tell us after the third.

So, thing are a bit tense at the start. McDonnell's not the only one missing. The organisers - the Hackney TUC and the Leabridge branch of the Labour party - are concerned that there aren't enough people in the audience. Then suddenly, it becomes clear that are going to be too many, and that people will have to be turned away for health and safety reasons.